Scientists Use Lasers To Trap, Study Atoms For First Time

July 19, 1986|The New York Times

NEW YORK -- Using seven beams of laser light, a team of scientists at AT&T Bell Laboratories has succeeded in slowing free atoms to a frozen crawl and trapping them in a space smaller than the period that ends this sentence.

The effort to confine atoms by the use of light has produced an intense competition over the last few years in the United States, the Soviet Union and Western Europe. Atomic physicists describe the achievement as a breakthrough that will make it possible to explore fundamental states of matter that have never before been observed.

``The light not only traps the atoms, but you can see them and study them,`` said Daniel Kleppner of the Massachusetts Institute of Technology. ``To me it`s breathtaking. It opens the way to observe with great clarity how atoms interact and how they evolve.``

In an ordinary vacuum chamber, crisscrossed beams create what the Bell scientists call ``optical molasses.`` Certain atoms that ordinarily move at miles per second were brought down to speeds slower than a person walks, making it possible to see their motion with the unaided eye.

The scientists say they have produced new records for cold and density in a gas. Because temperature depends on atomic motion, the process cools the atoms to within 250 millionths of a degree of absolute zero, vastly colder than can be achieved by ordinary refrigeration.

The most immediate application may come in improved atomic clocks. By relying on the natural vibrating of atoms, slicing time into intervals on the order of a billionth of a second, such clocks let navigation systems use satellite signals to fix global positions to within a few dozen yards. Because the resonance of slow atoms can be measured much more accurately, it may be possible to make atomic clocks much more precise.

Scientists also expect advances in a basic branch of physics that analyzes the spectral frequencies of the energy that different atoms radiate to determine the makeup of objects from rare chemicals to distant stars. The slowing of atoms should improve those spectroscopic measurements.

``There`s a new measurement day a-dawning,`` said John Hall, an expert on atomic clocks and spectroscopy at the National Bureau of Standards in Boulder, Colo. ``The chance to look at atoms for a long time, to see if every atom has same characteristics, to see if the gravity field of the earth has the effect we expect -- that`s the carrot that`s been hanging out in front of us for 10 years.``

But most of the excitement about the work at Bell Laboratories, discussed last week at a conference in Finland and scheduled to be reported in Physical Review Letters, concerns its potential for illuminating the deep questions of atomic reality that constitute quantum physics.

``The ability actually to trap atoms for the first time and manipulate them and move them around and watch them is quite important,`` said Theodor W. Hansch, an atomic physicist at the University of Munich. ``This is something people have been speculating about for some time. The hope is to discover fundamental interactions of trapped atoms among themselves or interactions with surfaces.``

Many physicists have been moving independently toward the same goal, including several American and French groups as well as theorists at the Institute for Spectroscopy in Moscow. The Soviet scientists have made important theoretical contributions but have lagged experimentally.

The researchers at Bell Laboratories, in Holmdel, N.J., captured about 500 atoms of sodium metal from a pellet that had been vaporized in a stainless steel vacuum chamber sprouting arms for video cameras and measuring instruments.

Six laser beams, shining from front and back, left and right, above and below, flood a cubic centimeter of space with radiation pressure that creates the optical molasses. That brings the atoms to a slow, random crawl.

A seventh needle-thin beam, tuned to a different frequency, exerts a different kind of light force. Instead of pushing on the atoms, the beam sets up an attraction based on the atoms` interaction with its energy field. In effect, it creates a tiny well into which the atoms fall.

``The atoms become like a moth, seeking out the region of higher laser intensity,`` said Steven Chu, head of quantum electronics research at the laboratory, who developed the technique with Arthur Ashkin, John Bjorkholm and Alex Cable.